1. Field of the Invention
The present invention relates to a touch panel type pressure sensitive writing tablet for displaying characters and lines input by a user using a touch panel, a method of controlling this pressure sensitive writing tablet, a program for controlling this pressure sensitive writing tablet, and electronic paper.
2. Background of Related Art
Touch panels are widely used in machines such as automatic teller machines (ATMs) at banks, and ticket vending machines at train stations. The user touches a selected icon or item, typically with a finger, to enter a corresponding instruction to the machine.
A touch panel may be used as a medium for writing characters and pictures on electronic paper. When an icon or item is selected by touching the surface of the touch panel (hereinafter referred to as xe2x80x9ctouch surfacexe2x80x9d) with a finger, or when characters are written on a blackboard-sized touch screen, the shortest distance between adjacent touch locations that can be identified and detected on the touch panel may be relatively great. However, when the pressure sensitive writing tablet is applied to electronic paper the size of A4, for example, the shortest distance between adjacent touch locations that can be identified and detected should be greatly reduced, and it is necessary to use a writing stylus comparable to a ball-point pen or a mechanical pencil in size.
The following problems arise when inputting characters and lines on a touch panel using such a pen-like writing stylus.
(a) When inputting a line on a touch panel with a writing stylus, the pressure applied to the touch panel by the writing stylus often varies because the touch surface is relatively slippery, which would produce a number of touch locations along the input line where the stylus pressure is below the threshold value for detection, and no touch is recognized at such positions. As a result, touch locations are actually detected at intervals. If the input line is displayed with the detected touch locations only, it would differ significantly from the one that the user intended to input.
(b) When the user holds the writing stylus by hand and presses the tip of the stylus against the touch surface to write characters or lines, a portion of the hand also contacts the touch surface. The touch panel must then distinguish a touch by the writing stylus from a touch by a portion of the hand. However, if the threshold value for detecting a touch on the touch surface is lowered to overcome the problem described in (a) above, useless contact from a portion of the hand having nothing to do with the input line would also be detected as an intended touch, and the line that is actually displayed would not match the input line intended by the user.
(c) Touches and their touch locations are detected based on digital values which are obtained by converting thereto, with an analog/digital converter (ADC), voltages across pressure sensitive resistors wired in a grid form in vertical and horizontal directions of the touch surface. The number of pressure sensitive resistors in the touch surface of, for example, a 12-inch touch panel used for inputting characters may be approximately 100xc3x97100. Assuming that a drive voltage for each pressure sensitive resistor is 5 V, the voltage change across the pressure sensitive resistor due to a touch at one touch location is extremely low, that is, approximately 0.0005 V, and the ADC output is extremely low. If the touch sensitivity of the touch panel is increased in order to resolve the above problem (a), the drive voltage must be significantly increased. This significantly increases power consumption of the touch panel.
(d) The touch locations detected by the touch panel may fluctuate, and when the detected touch locations are sequentially connected in the detected order with straight lines, the displayed line may become a crooked line consisting of very small line segments, which is different from the input line intended by the user.
An object of the present invention is to provide a pressure sensitive writing tablet capable of improving line input with a touch panel, electronic paper provided with the pressure sensitive writing tablet, a method for controlling the pressure sensitive writing tablet, and a program for making a computer execute the method.
Another object of the invention is to provide a pressure sensitive writing tablet that can faithfully display an input line without particularly increasing touch panel sensitivity, electronic paper provided with the pressure sensitive writing tablet, a method for controlling the pressure sensitive writing tablet, and a program for making a computer execute the method.
A further object of the invention is to provide a pressure sensitive writing tablet that can effectively prevent the touch locations from fluctuating, electronic paper provided with the pressure sensitive writing tablet, a method for controlling the pressure sensitive writing tablet, and a program for making a computer execute the method.
A pressure sensitive writing tablet according to a first aspect of the present invention comprises:
a touch panel for generating an output signal corresponding to a touch surface pressure distribution relating to touch locations where a writing stylus touched the touch surface;
means for generating touch data including data on a touch location and a touch time for each touch of the writing stylus to the touch surface by sampling the output signal of the touch panel, determining if there was a touch of the writing stylus to the touch surface based on the sampled data, and, if there was a touch, detecting the touch location and touch time of the touch;
means for determining, based on the touch data, whether each touch of the touch data is a touch on a contiguous line input on the touch panel;
means for generating velocity data by calculating, based on the touch data, a velocity of the writing stylus at each segment of the contiguous line input on the touch surface, the velocity data including data relating to the calculated velocities;
means for determining, based on the velocity data, a type of a line connecting the touch locations of two touches that are on the contiguous line and temporally adjacent to each other in the detection order (herein after referred to as xe2x80x9cadjacent touchesxe2x80x9d);
means for producing a line drawing connecting the touch locations of the respective adjacent touches based on the line types determined by the line type determining means; and
a display device for displaying the line drawing produced by the line drawing producing means.
The data on the touch locations and touch times included in the touch data may be the touch locations and touch times per se, or relative values for the touch locations and touch times. The relative values for the touch locations may include corrected touch locations used in the fluctuation suppression process described later. The relative values for the touch times may include, for example, the amount of time elapsed from a predetermined reference time which is represented by using a sampling time interval as a unit of measure, or may be sequence numbers assigned to the respective sampling times starting from a predetermined reference sampling time as n=1. The contiguous line input on the touch panel may be, for example, a partial line of a character, a line for drawing, or a line of a picture.
The display is typically a monochrome display. The correspondence between a unit of detection for the touch locations on the touch surface and a pixel on the display does not need to be 1:1. The distribution density of the unit of detection for the touch locations on the touch surface may be greater than or less than the distribution density of pixels on the display. That is, there may be a one-to-plural or plural-to-one correspondence in a partial or whole area between the unit of detection for the touch locations on the touch surface and the pixels on the display. The types of the connecting line determined by the line type determining means may include curves with different curvatures, a single line segment, and a crooked line consisting of plural (two or more) line segments.
The pressure sensitive writing tablet is typically a touch panel integrated with a display, but the touch panel and the display may be separately disposed. If the touch panel and the display are integrated, the touch panel must be transparent so that images on the display can be seen through the touch panel.
The velocity of the writing stylus moving on the touch surface when a contiguous line is input at touch locations is related to the type of the input contiguous line. By determining the type of the line connecting the touch locations associated with adjacent touches based on the velocity of writing stylus movement and displaying a line drawing produced based on the line type determined, a line faithful to the contiguous line input by the user can be displayed even when the touch locations are detected at intervals or with skips along the input contiguous line.
According to the first aspect of this invention, since the detected touches along the input contiguous line may be skipping, that is, it is not necessary to increase the detection sensitivity of the writing stylus for the touch locations in order to distinguish a touch and a non-touch, it is possible to avoid detecting unnecessary touches as a result of increasing the detection sensitivity, and to avoid increasing power consumption as a result of increasing the touch panel drive voltage.
According to the second aspect of the present invention, in the pressure sensitive writing tablet of the first aspect, the display device is disposed at a side opposite to the touch surface of the touch panel.
According to the third aspect of the present invention, in the pressure sensitive writing tablet of the first or second aspect, the line type determining means sets, as a connecting line between two touch locations of adjacent touches, a line having a less curvature when the velocity of the writing stylus between the two touch locations on the touch surface is high than when the velocity is low.
A single line segment has a curvature smaller than that of a curve or a crooked line. The velocity of the writing stylus at a touch position is relatively high when the input contiguous line is a straight or nearly straight line, and is relatively low when the contiguous line is a curve with a large curvature. It is expected that the velocity of the writing stylus on the touch surface is approximately 1.0 m/sec in the case of the straight or nearly straight line, while it is approximately 0.5 m/sec in the case of a general curve though the velocity would become smaller as the curvature becomes larger. It is, therefore, possible to display a line more faithful to the contiguous line input by the user by setting the type of the line connecting the touch locations of two adjacent touches to a line type having a smaller curvature, that is, a line similar to a single line segment, when the writing stylus velocity is high than when the velocity is low.
According to the fourth aspect of the present invention, in the pressure sensitive writing tablet of one of the first to third aspects, when the line type determining means determines that the writing stylus has moved on a curve between the adjacent touches, it defines the following,
C(0), C(1): earlier and later adjacent touches, respectively,
C(xe2x88x921): a touch one before C(0),
C(2): a touch one after C(1),
L1: a line connecting the touch locations of C(xe2x88x921) and C(0),
L2: a line connecting the touch locations of C(1) and C(2),
Ra: an intersection of L1 and L2; and
sets the line connecting C(0) and C(1) to a line type passing inside the sides of a triangle C(0)-Raxe2x80x94C(1).
Thus, the line connecting the touch locations for the adjacent touches has a controlled curvature so that a line faithful to the contiguous line input by the user can be displayed.
According to the fifth aspect of the present invention, in the pressure sensitive writing tablet of one of the first to fourth aspects, a time interval for detecting the output signal of the touch panel by the touch data generating means is shorter than the minimum time interval defined as the time required for a user to move the writing stylus by z on the touch panel, where z represents a shortest distance between touch locations which can be identified on the touch panel.
Typical specifications for the pressure sensitive writing tablet are as follow.
Touch surface and display size: 12 inches
Number of detectable touch locations on the touch surface in vertical and horizontal directions: 1000xc3x971000
Number of display pixels in vertical and horizontal directions: 1000xc3x971000
Sampling frequency: 400-800 Hz
Serial data transfer rate from an ADC when the touch panel output is converted from analog to digital by the ADC: 9600-19,200 bps
Since the time interval for detecting the output signal of the touch panel by the touch data generating means is shorter than the minimum time interval defined as the time required for the user to move the writing stylus by z on the touch panel, touches having consecutive touch locations can be reliably detected insofar as the touch pressure is equal to or greater than a predetermined threshold value.
A pressure sensitive writing tablet according to the sixth aspect of the present invention comprises:
a touch panel for generating an output signal corresponding to a touch surface pressure distribution relating to touch locations where a writing stylus touched the touch surface;
means for generating primary touch data including data on a primary touch location and a touch time for each touch of the writing stylus to the touch surface by sampling the output signal of the touch panel, determining if there was a touch of the writing stylus to the touch surface based on the sampled data, and, if there was a touch, detecting the touch location and touch time of that touch;
means for determining, based on the primary touch data, whether each touch of the primary touch data is a touch on a contiguous line input on the touch panel;
means for generating secondary touch data including data on a secondary touch location for each touch by computing the secondary touch location which is obtained from correcting, by a predetermined correction process, a primary touch location of a touch included in the primary touch data and located on the contiguous line (hereinafter referred to as xe2x80x9ctarget touchxe2x80x9d) based on primary touch locations of multiple touches (hereinafter referred to as xe2x80x9ccorrecting touchesxe2x80x9d) having the respective touch times within a predetermined time range Ta including the touch time of the target touch;
means for producing a line drawing connecting with a selected line the secondary touch locations of two touches that are on the contiguous line and temporally adjacent to each other in the detection order (hereinafter referred to as xe2x80x9cadjacent touchesxe2x80x9d); and
a display device for displaying the line drawing produced by the line drawing producing means.
The correcting touches are limited to those within the predetermined time range Ta from the touch time of the target touch. Representing the touch time of the target touch by to, and defining a predetermined value DT, then Ta may be
to xe2x88x92xcex94Txe2x89xa6Taxe2x89xa6to+xcex94T; or 
to xe2x88x92xcex94Txe2x89xa6Taxe2x89xa6to; or 
to xe2x89xa6Taxe2x89xa6to+xcex94T. 
Since a touch location for a touch with a touch time far from the touch time of the target touch has little effect on the touch time of the target touch, it is advantageous to limit the correcting touches to those within the predetermined time range Ta.
Since the writing stylus often slips on the touch surface, touches on the touch surface by the writing stylus may wander or fluctuate. If the line drawing is produced and displayed based on the primary touch locations subject to such fluctuation, the displayed line would deviate from the line intended by the user. Therefore, the secondary touch locations are generated by the correction process for suppressing such fluctuation, and the line drawing is produced and displayed based on these secondary touch locations. As a result, deviation from the intended line, or fluctuation, can be suppressed in the displayed line, that is, the displayed line is faithful to the line intended by the user.
According to the seventh aspect of the present invention, in the pressure sensitive writing tablet of the sixth aspect, the correcting touches used in the correction process are touches at primary touch locations in a predetermined area Ao containing the primary touch location of the target touch.
The predetermined area Ao may be, for example, a circle having a predetermined radius or a square having a predetermined side length, centered on the primary touch location of the target touch.
Change in touch locations due to the fluctuation is relatively small. If the change is large, it is considered that the change has occurred due to an intentional movement of the writing stylus rather than the fluctuation. Therefore, by limiting the correcting touches to the primary touch locations within the predetermined area Ao, secondary touch locations appropriate for use in suppressing the fluctuation can be calculated.
According to the eighth aspect of the present invention, in the pressure sensitive writing tablet of the sixth or seventh aspect, the correction process counts for each primary touch location the number of correcting touches having the same primary touch location, and selects a primary touch location having the highest count as a secondary touch location for the target touch.
Touches due to the fluctuation are exceptional or infrequent, and most touches are presumed to be the ones which are not affected by the fluctuation. Therefore, by setting the secondary touch location for the target touch to the primary touch location having the maximum number of correcting touches, the fluctuation has no or little influence on the secondary touch location for the target touch.
According to the ninth aspect of the present invention, in the pressure sensitive writing tablet of the eighth aspect, the correction process computes an average position of the primary touch locations of the correcting touches, and selects this average position as the secondary touch location for the target touch if there is no primary touch location having the highest count.
There may be a case in which a primary touch location having the maximum number of correcting touches sharing the same primary touch location is not found because the secondary touch locations of the correcting touches are dispersed. In such a case, the fluctuation can be appropriately suppressed by using the average position of the secondary touch locations of the correcting touches as the secondary touch location for the target touch.
According to the tenth aspect of the present invention, the pressure sensitive writing tablet of one the sixth to ninth aspects further comprises:
means for generating velocity data by calculating, based on the touch data, a velocity of the writing stylus at each segment of the contiguous line input on the touch surface, the velocity data including data relating to the calculated velocities; and
means for determining, based on the velocity data, a type of a line connecting the secondary touch locations of the adjacent touches.
Thus, by displaying a line drawing produced based on the secondary touch locations calculated by the correction process, a line closer to the input continuous line intended by the user can be displayed.
According to the eleventh aspect of the present invention, in the pressure sensitive writing tablet of one of the sixth to tenth aspects, the display device is provided at a side opposite to the touch surface of the touch panel.
According to the twelfth aspect of the present invention, in the pressure sensitive writing tablet of one of the sixth to eleventh aspects, the line type determining means sets, as a connecting line between two touch locations of adjacent touches, a line having a less curvature when the velocity of the writing stylus between the two touch locations on the touch surface is high than when the velocity is low.
According to the thirteenth aspect of the present invention, in the pressure sensitive writing tablet of one of the sixth to twelfth aspects, when the line type determining means determines that the writing stylus has moved on a curve between the adjacent touches, it defines the following:
C(0), C(1): earlier and later writing stylus touches, respectively,
C(xe2x88x921): a touch one before C(0),
C(2): a touch one after C(1),
L1: a line connecting the touch locations of C(xe2x88x921) and C(0),
L2: a line connecting the touch locations of C(1) and C(2),
Ra: an intersection of L1 and L2.
The line type determining means then sets the line connecting C(0) and C(1) to a line type passing inside the sides of a triangle C(0)-Raxe2x80x94C(1).
According to the fourteenth aspect of the present invention, in the pressure sensitive writing tablet of one of the sixth to thirteenth aspects, a time interval for detecting the output signal of the touch panel by the touch data generating means is shorter than the minimum time interval defined as the time required for a user to move the writing stylus by z on the touch panel, where z represents a shortest distance between touch locations which can be identified on the touch panel.
Electronic paper according to the fifteenth aspect of the present invention comprises the pressure sensitive writing tablet of one of the first to fourteenth aspects. The electronic paper may be defined as being substantially identical in appearance and handling to conventional paper, except that lines and characters are written using the pressure from a pen point instead of ink.
A method for controlling a pressure sensitive writing tablet according to the sixteenth aspect of the present invention comprises the steps of:
generating an output signal corresponding to a touch surface pressure distribution relating to touch locations where a writing stylus touched the touch surface;
generating touch data including a touch location and a touch time for each touch of the writing stylus to the touch surface by sampling the output signal generated by the output signal generating step, determining if there was a touch of the writing stylus to the touch surface based on the sampled data, and, if there was a touch, detecting the touch location and touch time of the touch;
determining, based on the touch data, whether each touch of the touch data is a touch on a contiguous line input on the touch panel;
generating velocity data by calculating, based on the touch data, a velocity of the writing stylus at each segment of the contiguous line input on the touch surface, the velocity data including data relating to the calculated velocities;
determining, based on the velocity data, a type of a line connecting the touch locations of two touches that are on the contiguous line and temporally adjacent to each other in the detection order (hereinafter referred to as xe2x80x9cadjacent touchesxe2x80x9d);
producing a line drawing connecting the touch locations of the respective adjacent touches based on the line types determined by the line type determining step; and
displaying the line drawing produced by the line drawing producing step.
According to the seventeenth aspect of the present invention, in the method for controlling a pressure sensitive writing tablet of the sixteenth aspect, the displaying step preferably displays at the back of the touch panel.
According to the eighteenth aspect of the present invention, in the method for controlling a pressure sensitive writing tablet of the sixteenth or seventeenth aspect, the line type determining step sets, as a connecting line between two touch locations of adjacent touches, a line having a less curvature when the velocity of the writing stylus between the two touch locations on the touch surface is high than when the velocity is low.
According to the nineteenth aspect of the present invention, in the method for controlling a pressure sensitive writing tablet of one of the sixteenth to eighteenth aspects, when the line type determining step determines that the writing stylus has moved on a curve between the adjacent touches, it defines the following:
C(0), C(1): earlier and later adjacent touches, respectively,
C(xe2x88x921): a touch one before C(0),
C(2): a touch one after C(1),
L1: a line connecting the touch locations of C(xe2x88x921) and C(0),
L2: a line connecting the touch locations of C(1) and C(2),
Ra: an intersection of L1 and L2.
The line type determining step then sets the line connecting C(0) and C(1) to a line type passing inside the sides of a triangle C(0)-Raxe2x80x94C(1).
According to the twentieth aspect of the present invention, in the method for controlling a pressure sensitive writing tablet of one of the sixteenth to nineteenth aspects, a time interval for detecting the output signal of the touch panel by the touch data generating step is shorter than the minimum time interval defined as the time required for a user to move the writing stylus by z on the touch panel, where z represents a shortest distance between touch locations which can be identified on the touch panel.
A method for controlling a pressure sensitive writing tablet according to the twenty-first aspect of the present invention comprises the steps of:
generating an output signal corresponding to a touch surface pressure distribution relating to touch locations where a writing stylus touched a touch surface of a touch panel;
generating primary touch data including data on a primary touch location and a touch time for each touch of the writing stylus to the touch surface by sampling the output signal of the touch panel, determining if there was a touch of the writing stylus to the touch surface based on the sampled data, and, if there was a touch, detecting the touch location and touch time of that touch;
determining, based on the primary touch data, whether each touch of the primary touch data is a touch on a contiguous line input on the touch panel;
generating secondary touch data including data on a secondary touch location for each touch by computing the secondary touch location which is obtained from correcting, by a predetermined correction process, a primary touch location of a touch included in the primary touch data and located on the contiguous line (hereinafter referred to as xe2x80x9ctarget touchxe2x80x9d) based on primary touch locations of multiple touches (hereinafter referred to as xe2x80x9ccorrecting touchesxe2x80x9d) having the respective touch times within a predetermined time range Ta including the touch time of the target touch;
producing a line drawing connecting with a selected line the secondary touch locations of two touches that are on the contiguous line and temporally adjacent to each other in the detection order (hereinafter referred to as xe2x80x9cadjacent touchesxe2x80x9d); and
displaying the line drawing produced by the line drawing producing step.
According to the twenty-second aspect of the present invention, in the method for controlling a pressure sensitive writing tablet of the twenty-first aspect, the correcting touches of the correction process are preferably touches with a primary touch location in a predetermined area Ao containing the primary touch location of the target touch.
According to the twenty-third aspect of the present invention, in the method for controlling a pressure sensitive writing tablet of the twenty-first or twenty-second aspect, the correction process counts for each primary touch location the number of correcting touches having the same primary touch location, and selects a primary touch location having the highest count as a secondary touch location for the target touch.
According to the twenty-fourth aspect of the present invention, in the method for controlling a pressure sensitive writing tablet of the twenty-third aspect, the correction process computes an average position of the primary touch locations of the correcting touches, and selects this average position as the secondary touch location for the target touch when there is no primary touch location having the highest count.
According to the twenty-fifth aspect of the present invention, the method for controlling a pressure sensitive writing tablet of one of the twenty-first to twenty-fourth aspects further comprises the steps of:
generating velocity data by calculating, based on the touch data, a velocity of the writing stylus at each segment of the contiguous line input on the touch surface, the velocity data including data relating to the calculated velocities; and
determining, based on the velocity data, a type of a line connecting the secondary touch locations of the adjacent touches.
According to the twenty-sixth aspect of the present invention, in the method for controlling a pressure sensitive writing tablet of one of the twenty-first to twenty-fifth aspects, the displaying step displays at the back of the touch panel.
According to the twenty-seventh aspect of the present invention, in the method for controlling a pressure sensitive writing tablet of the twenty-fifth aspect, the line type determining step sets, as a connecting line between two touch locations of adjacent touches, a line having a less curvature when the velocity of the writing stylus between the two touch locations on the touch surface is high than when the velocity is low.
According to the twenty-eighth aspect of the present invention, in the method for controlling a pressure sensitive writing tablet of the twenty-seventh aspect, when the line type determining step determines that the writing stylus has moved on a curve between the adjacent touches, it defines the following:
C(0), C(1): earlier and later writing stylus touches, respectively,
C(xe2x88x921): a touch one before C(0),
C(2): a touch one after C(1),
L1: a line connecting the touch locations of C(xe2x88x921) and C(0),
L2: a line connecting the touch locations of C(1) and C(2),
Ra: an intersection of L1 and L2.
The line type determining step then sets the line connecting C(0) and C(1) to a line type passing inside the sides of a triangle C(0)-Raxe2x80x94C(1).
According to the twenty-ninth aspect of the present invention, in the method for controlling a pressure sensitive writing tablet of one of the twenty-first to twenty-eighth aspects, a time interval for detecting the output signal of said touch panel by said touch data generating means is shorter than the minimum time interval defined as the time required for a user to move the writing stylus by z on said touch panel, where z represents a shortest distance between touch locations which can be identified on said touch panel.
A control program for a pressure sensitive writing tablet according to the present invention makes a computer execute the steps of the method for controlling the pressure sensitive writing tablet of one of the sixteenth to twenty-ninth aspects.